Cancer is among the largest causes of death in our patients and remains a significant concern for pet owners of aging pets. The true incidence of cancer is not well established, however, based on necropsy studies, nearly half of all dogs over the age of ten die of cancer. How can we work to decrease these statistics?
In human oncology, several tests are recommended either based on age or based on cancer risk, to screen for cancer. Our primary types of cancer differ, and genetic testing is limited. As a result, there is limited assessment of these screening tests for specific cancers in dogs and cats. However, as we attempt to bring further awareness to the risks and outcomes associated with cancer in our patients, utilizing tests that we do every day could help us detect cancer at an earlier point in time.
Earlier intervention and treatment of cancer allows for the best long-term outcome and potential for cure, regardless of the species.
Below are five common diagnostic techniques available in most hospitals that can help you diagnose cancer earlier in dogs and cats.
Fine needle aspirate of masses
If new lumps or bumps are noted, obtaining a fine needle aspirate (FNA) can provide valuable information in an affordable and non-invasive way. It is also important to monitor masses over time. Completing a body map for individual patients can be helpful to allow for measuring and quickly assessing a change overtime. Even benign tumors over time can necessitate treatment, including lipomas which can become infiltrative or reflect liposarcomas. Therefore, obtaining a thorough body map on all senior pets could be of value.
A valuable part of the physical exam, especially in senior pets is a rectal exam. This can aide in identification anal sac tumors at smaller sizes or potentially before clinical signs are noted. Approximately 40% of these tumors are found incidentally. As our patients often don’t tell us what ails them, a thorough physical exam to screen for cancer can be critical in early detection.
It is common for senior pets to have annual lab work. Although cancer is not always readily detectable in routine lab work, there are some potential red flags.
The complete blood count– The complete blood count can provide valuable details with regards to the overall health of the patient and potential recommendations for further investigation. It is important to evaluate a complete differential for the most comprehensive information. In addition, a reticulocyte count, either obtained as part of a complete blood count or requested, is critical in understanding the anemic patient. The incidence of anemia in our patients secondary to cancer is not well established. However, the incidence is reported 25-30% in humans and likely similar paraneoplastic incidence in veterinary oncology.
Other cell lines can provide valuable information with regards to cancer. An elevated lymphocyte count can be further investigated with non-invasive testing. Flow cytometry is a valuable screening test to aide in the diagnosis and classification of lymphoproliferative disorders. Flow cytometry takes live cells and applies labeled antibodies to them to classify cells. In the case of an elevated lymphocyte count, flow cytometry along with a pathologist review share diagnostic utility in cases of chronic leukemia or more aggressive disease such as acute leukemia and lymphoma. This test as a diagnostic aide can be performed on blood and cavity fluids, as well as tissues such as lymph nodes, bone marrow, and organ aspirates. Valuable information for flow cytometry including applications of, submission recommendations, and step by step instructions can be found via Colorado State University’s microbiology, immunology, and pathology website. Most commercial laboratories now offer flow cytometry as well.
Chemistry profile– The accompanying chemistry profile can lead to further interrogation of sites of cancer. Red flags for cancer include hypercalcemia and hyperglobulinemia. The most common cancer associated with hyperglobulinemia is multiple myeloma. Patients affected with this cancer have a variety of clinical signs, but it is important to note, hyperglobulinemia can also be an incidental finding. Another common chemistry profile finding associated with multiple myeloma in cats is hypocholesterolemia, reported in 68% of cats. Hypercalcemia in dogs is most commonly secondary to neoplasia. Specifically, 2/3 of dogs with hypercalcemia are secondary to cancer. The most common cancers associated with hypercalcemia include lymphoma, anal sac apocrine gland adenocarcinoma, and multiple myeloma. To obtain these key markers for potential cancer, a complete chemistry profile is recommended and ideally on a fasted patient. Tying these findings in with a thorough physical exam is critical in the diagnosis and screening for cancer.
The third facet of the minimum database for lab work is the urinalysis.This provides an exciting opportunity to utilize a true screening test for a cancer that previously could be challenging to diagnose. Transitional cell carcinoma (TCC) is the most common tumor of the urogenital system in dogs. There are certain breeds that are more commonly affected that you may already be recommending early screening with abdominal ultrasounds.
However, we now have the ability to test for this cancer using a simple urine sample. The test is evaluating for a mutation in the BRAF gene, which has been shown to be involved in a number of human malignancies and was identified as a mutation in 85% of canine urogenital cancers. The test is available through Sentinel Biomedical and is highly sensitive, requiring a fraction of mutated cells to provide a positive test. Clinically, this can provide diagnosis months prior to a patient showing clinical signs or a sizable mass effect. Often, the clinical signs associated with TCC are treated symptomatically, delaying early aggressive treatment. This test, unlike the previously utilized bladder tumor antigen test, is not impacted by hematuria, pyuria, or proteinuria in the urine.
A screening opportunity for early cancer detection includes thoracic radiographs. Primary lung tumors in dogs are identified ~30% of the time incidentally in patients without any clinical signs. In a recent study of primary pulmonary histiocytic sarcoma, 25% of cases were incidental findings. Patients without clinical signs likely have less advanced disease, allowing for surgery, the most successful treatment for primary lung tumors, regardless of origin. It is also possible to detect pulmonary metastasis as an incidental finding.
We encourage everyone to facilitate exams and potential screening tests for your aging and at-risk patients. The earlier we find cancer, the greater chance for improved prognosis and potentially a Cure.
Carcinoma of the apocrine glands of the anal sac in dogs: 113 cases (1985-1995). JAVMA 2003
Prevalence and disease associations in feline thrombocytopenia: a retrospective study of 194 cases. JSAP September 2018
Multiple Myeloma in 16 cats: a retrospective study, Vet Clin Path 2005
Sentinel Biomedical https://www.sentinelbiomedical.com/braf-vets/
Primary pulmonary histiocytic sarcoma in dogs: A retrospective analysis of 37 cases. VCO 2018, epub.